The present invention relates to a multi-position rotary switch and more particularly to a rotary switch using radiation emitters and detectors where a rotatable drum coded with reflective and non-reflective areas is used to actuate the switch.
Various forms of optical switches are known in the prior art. For example, U.S. Pat. No. 3,603,982 discloses a data entry or keyboard type switch arrangement using reflected light as a means of encoding characters. Each character is represented by a key on the keyboard. For each character, a photosensitive device is also provided, located in alignment with the corresponding data entry element in a lightproof housing. A light source is provided in the housing to provide illumination between the keys and the photosensitive devices. A reflective surface mounted on an angle on each key intercepts light from the light source and reflects it onto the photosensitive device corresponding to the key when the key is actuated. A signal is thereby produced which is effective, through a logical encoding network, to produce an output signal representing the character corresponding to the actuated key. In this arrangement, a separate reflector is provided for each key.
U.S. Pat. No. 3,697,762 provides a single keyswitch having a light emitting diode and light-sensing element arranged in side-by-side relation. A light reflecting element is arranged so that when it is passed into the path of radiant energy emanating from the light emitting diode, a portion of the light beam is reflected to the light-sensing element so as to initiate an "on" or an "off" function. Each keyswitch is a self-contained unit requiring its own reflecting element, light emitter, and light detector.
U.S. Pat. No. 3,886,544 discloses a keyboard using optical switching. Light is transmitted and received by fiber optic conductors. Actuation of a keyswitch brings a reflector into view of the fiber optic conductors, thereby completing a switching function.
Another prior art arrangement using fiber optics is shown in U.S. Pat. No. 4,045,667. This patent relates to a color-sensitive photoelectric control system where different switching functions are actuated using color coded light. In U.S. Pat. No. 4,340,813 a switch panel with touch switches is disclosed. Radiation is reflected or dispersed when a switch space is touched so that sensors are actuated by the dispersed radiation.
The prior art does not disclose a multi-position rotary switch using the reflection and detection of radiation to indicate switch actuations. It would be advantageous to provide such a rotary switch which is simple in design, highly reliable, and relatively inexpensive to manufacture. It would be further advantageous to provide such a switch with a coded output, such as binary coded decimal ("BCD"), to provide simple interface to an external electronic circuit in which the switch is used.
The present invention provides such a multi-position rotary switch using an actuator drum coded with reflective and non-reflective areas. The switch uses reflective surfaces to complete optical circuits and non-reflective surfaces to inhibit the completion of such circuits. In a preferred embodiment, the rotary switch of the present invention uses an actuator drum divided into a plurality of different n-bit codes where each bit is represented by a reflective area or a non-reflective area on the drum. A separate emitter-detector pair is arranged to emit radiation and detect radiation from each different bit of the n-bit codes. Each different n-bit code detected by the emitter-detector pairs as the actuator drum is rotated is indicative of a particular switch position.